Calendar 2030 — End-of-Decade Yearly Grid With Holidays

Why 2030 Matters — A Civilizational Hinge

In 2026, a strategist at the United Nations Sustainable Development Goals secretariat needs a 2030 calendar with both US and Indian holidays to coordinate the final SDG review summit — every major framework set in 2015 (Paris Agreement NDCs, SDGs 1-17, EU 2030 Climate Target Plan) culminates this year, and the working calendar is the primary planning artifact.

The Gregorian calendar we still use was promulgated by Pope Gregory XIII in February 1582 to correct the Julian drift of about 11 minutes per year. By 1582 that drift had accumulated to ten days — Pope Gregory simply dropped them: Oct 4, 1582 was followed by Oct 15. Britain and its American colonies didn't adopt the reform until 1752 (Calendar Act of 1750), Russia not until 1918, Greece in 1923.

Zeller's congruence — published by Christian Zeller in 1882 (the original paper "Kalender-Formeln") — gives the closed-form weekday of any Gregorian date. The formula uses floor functions over months, year-of-century, and century. Modern JavaScript Date objects internally use a derived algorithm; our SVG month grids cross-check both methods to render the correct first-of-month weekday.

The Uniform Monday Holiday Act, signed by Lyndon B. Johnson on June 28, 1968, shifted Washington's Birthday, Memorial Day, and Columbus Day to Mondays starting in 1971. That is why Memorial Day always lands on the last Monday of May, and Labor Day on the first Monday of September. In 2030 these fall on May 27 and September 2 respectively.

India's national holidays are governed by the Ministry of Personnel, Public Grievances and Pensions, with Republic Day (January 26) commemorating the 1950 adoption of the Constitution and Independence Day (August 15) marking the 1947 partition. Diwali, Holi, and Vaisakhi follow the Drik Panchang lunisolar calendar — dates shift year to year and are confirmed by Government of India gazette notification roughly six months ahead.

ISO 8601, first published in 1988 and most recently revised in 2019, defines week numbering: week 1 contains the year's first Thursday. For 2030, week 1 runs Monday December 31, 2029 through Sunday January 6, 2030. The ISO weekday number runs 1 (Monday) to 7 (Sunday) — not the JavaScript 0-6 convention, a common source of bugs.

For more, see days until any date, holiday calendar, and ISO date converter.